The problem of providing impedances with highly precise values is encountered in numerous applications where part of the integrated circuit is analog in type. For example, to make integrated delay circuits, time constant circuits of the resistor-capacitor type are used, and to retain a precise value of the time constant, the resistive and capacitive elements of the circuit must have highly precise values.
Another important application is in integrating circuit transceivers that serve to transmit signals by way of transmission lines. It is then generally necessary to provide the receiver side with an adaptation impedance the value of which is equal to the characteristic impedance of the line, in order to suppress or limit signal reflection. In embodiments known thus far, the adaptation impedance is external to the integrated circuit, precisely because of the difficulty of making impedances that have a highly precise value. However, if one wishes to make an integrated transceiver capable of functioning at high speed, for example on the order of 1 Gbit/s, using an external adaptation impedance involves difficulties, due in particular to the parasitic inductances introduced by the connections between the internal impedance and the terminals of the integrated circuit. Consequently, it would be desirable to be able to make an integrated adaptation impedance, but the problem of being able to precisely adjust its value is still encountered.
It is known that precise dimensioning of the components belonging to an integrated circuit does not make it possible to obtain precise characteristics of these components, because of process variations and drift of characteristics from aging or temperature changes.